Laser interference lithography is a low-cost method for the exposure of large
surfaces with regular patterns. Using this method, microsieves with a pore
size of 65 nm and a pitch of 200 nm have been fabricated. The pores are
formed by inverting a square array of photoresist posts with a chromium
lift-off process and by subsequent reactive-ion etching using the chromium
as an etch mask. The method has wider process latitude than direct
formation of holes in the resist layer and the chromium mask allows for
etching of pores with vertical sidewalls.